A. Field Of Invention
The present invention relates to signaling in a telecommunication network and the processes by which telephone calls are established in a telecommunication network. More specifically, it relates to a method and protocol using R2 signaling for connecting data calls originating from computers or other data terminals, and which are destined for receipt by a host computer system.
The methods disclosed herein are performed by an element of communications equipment called a Network Access Server ("NAS"), which is connected to a host computer system, typically through a network. The network access server provides numerous individual dial-up modem connections to a network such as a LAN or WAN. The NAS interfaces with a by way of multiplexed trunk lines, and then routes the data to a host computer over the network. Network access servers are well-known devices, and are widely available from companies such as 3Com Corporation, Livingston Enterprises, and Ascend, to name a few.
B. Description of Related Art
The R2 protocol is a signaling protocol in an inter-register family of signaling systems standardized by the International Telecommunications Union-Telecommunication Standardization Sector ("ITU-T", formerly known as the CCITT). R2 is used mostly in Europe and other regions in the world, but is not used in North America. The "R" stands for Regional standard recommendation and includes ITU-T Q-series standards, Q.400 to Q.490 and the "2" stands for the second regional standard. R2 is used over trunks in an international telecommunications system. As is known in the telecommunication arts, a trunk is a circuit connecting two switching elements such as telecommunication exchanges. Trunks are combined into trunk groups, creating a high capacity circuit capable of transmitting multiple channels of information between two telecommunication exchanges.
The R2 protocol is broken down into two parts: line signaling; and register signaling. Line signaling coveys call status information about a state of a call such as off-hook, on-hook, busy, etc. with call setup and call tear down states (e.g., idle, seize, seize acknowledgment, answered, clear-back, clear-forward and blocked). Register signaling, also known as Multi-Frequency Compelled ("MFC") signaling, is used for addressing. It conveys an ANI ("Automatic Number Identification", i.e., a calling number) and a DNIS ("Dialed Number Identification Service", i.e., a called number), a calling party's category and other network connections with handshaking or an acknowledgment process that includes "forward" (i.e., send) and "backward" (i.e., receive) signals. A forward signal is the signal transmitted by an R2 outgoing register to a remote R2 incoming register. When the signal is confirmed by an R2 incoming register, a backward signal is then transmitted back to the R2 outgoing register.
In a digital transmission system, four bits of a Time Division Multiplexing ("TDM") time slot on a multi-channel trunk are used for R2 signaling, two signaling bits per voice channel. As is known in the telecommunication arts, an ITU-T E1 has a bit rate of 2.048 Mega-bit-per-second ("Mbps") with 32 time slots of 8-bits each sampled every 125 microseconds (i.e., 32.times.8-bits/125.times.10.sup.-6 seconds=2.048 Mbps). Time-slot-zero is used for frame alignment and synchronization and time-slot-16 is used for signaling information. The remaining time-slots are used for voice information. The four R2 signaling bits include "Af" and "Bf" bits for forward signals, and "Ab" and "Bb" bits for backward signals and are used in time-slot-16 on an E1.
For register signaling in the MFC mode, compelled signaling is achieved by sending pairs of two out of six designated frequencies simultaneously. A maximum of six frequencies are used for signaling between international telecommunication exchanges. Different sets of frequencies are used for the forward and backward signals. This provides a total of 15 multi-frequency combinations in each direction (i.e., forward and backward) for a maximum of 30. Each combination number has a defined meaning of a signal that varies with different forward and backward groups. For example MFC-1 uses a frequency of 1,380 Hertz ("Hz") in the forward direction and a frequency of 1,020 Hz in the backward direction.
Forward signals consists of 15 combination numbers and include Group I signals for outgoing switch equipment control of a calling party and Group II signals for a calling party's category. Backward signals consists of 15 combination numbers and include Group A control signals to request forward signals that indicate the called party's line condition Group B and signals that indicate the state of a called party.
Group II and forward signals use the same frequencies as Group I signals. Group B backward signals use the same frequencies as Group A, but the meanings of the signals differ between the groups that use identical frequency pairs. For complete information on the combinations see the ITU-T R2 standard, Q.400-Q.490. R2 is typically used to create connections for voice calls sent over the multiple time slots in an E1.
There are several problems associated with using R2 signaling to create data connections. The R2 voice connection signals are numerous and many of the signals are not necessary if a party desires to make a data connection instead of a voice connection. Using R2 voice connection signals to make a data connection unnecessarily increases the complexity of a R2 signaling system.
Another problem with R2 voice signals is that individual countries may require special R2 signals to interface with their own unique telecommunication equipment for voice connections. Additional special R2 signals may also be required to complete data connections to interface with a country's telecommunications equipment. This increases the number of R2 signals that need to be interpreted.
Yet, another problem with using existing R2 voice signaling to make a data call is that the R2 forward register signals require a tone decoder to decode the available R2 forward register signals. This increases the cost of making a data connection if voice connections will not be made.